Art of road construction



Fatented May 29, 1934 TENT FFHCE ART OF ROAD CONSTRUCTION Francis L. Carson, San Francisco, Calif., assignor to The Pacific Lumber Company, San Francisco, Calif., a corporation of Maine No Drawing. Application December 16, 1930, Serial No. 502,871

8 Claims.

The present invention relates to improvements in the art of road construction. The invention has particular reference to that type of road construction wherein an asphalt coating is applied to crushed rock or other aggregate.

A principal object of my invention is to prepare the asphalt in the refinery in such a manher that it may be readily emulsified with water at a distant point where it is to be applied to the i0 road, and hence effect a large saving in freight since it is unnecessary by my method to transport water long distance or to pay for elaborate and costly methods of emulsification at the point of origin.

Another object of my invention is to effect the emulsification of a high melting point asphalt used in the construction of the road with a small amount of a fatty acid.

Another object of my invention is to prepare an emulsion of the irreversible oil in water type.

Another object of my invention is to prepare an asphalt emulsion which is readily decomposed or broke into its components, that is to say, I prepare an asphalt emulsion which may be readily de-emulsified. Another object of my invention is to construct an asphaltic paving containing shredded redwood bark, the shreds of the latter being approximately three inches in length, which shredded redwood bark is scattered over the surface of the rock prior to the application of the asphalt surface, or alternatively, the shredded redwood bark may be mixed with the rock as the latter is spread over the sub-grade or at any convenient point prior thereto. The function of the shredded redwood bark is to reinforce the union between the mineral aggregate and the asphalt and thereby lessen the tendency to slippage of the asphaltic pavement.

With these and other objects in view, my invention involves the construction of asphaltic pavements by applying to crushed rock an asphaltic emulsion, the asphalt content of the said emulsion being as high as 55% by weight of the entire emulsion and the said asphalt itself having a thin liquefaction point of from 212 to 350 F.

Prior to my invention, the asphalts most commonly used in road construction emulsions were those which were liquid at normal atmospheric temperatures, or which were thinly liquid at temperatures slightly above 100 F. and these are all too soft to be of a satisfactory character for this purpose.

,The emulsification of such asphalts has been thoroughly worked out, and it is quite common practice to effect the emulsification of the same, using a soap or a clay as the dispersing agent. My invention has nothing to do with the preparation of emulsions from liquid or low melting point asphalts, in which soap or clay is added to the water which is to become the external phase. My invention has two characteristics distinguishing it from the prior practice, which are (l) the preparation of an asphalt emulsion from an asphalt of high melting point, which asphalt may be represented by that type commonly known as D grade asphalt, which will be more fully identified hereinafter, and (2) the fact that I provide a method whereby .the asphalt is subjected to chemical treatment at the refinery, and thereby rendered emulsifiableat the distant point where the emulsion is to be applied to the pavement, by merely adding the molten asphalt to a hot solution containing caustic soda. 7

In order to point out the practical utility of my invention, particularly as regards the second characteristic noted above, wherein 9. treated asphalt is shipped to the point where it is to be applied to the road and emulsified at that point, the following data is given as to costs.

The price of asphalt at the refinery is about $12.00 per ton. It has been determined by a study of various data that the average freight cost per ton for asphalt shipped on the Pacific coast is $6.00. This high freight charge is due to the fact that the Pacific coast is not densely populated and it is often necessary to ship asphalt long distances from the principal refinery to the points where it is to be used. The price of a 50% emulsion at the refinery is approximately that of pure asphalt. In other words, when one purchases a ton of 50% asphalt emulsion, he is virtually paying $24.00 per ton for the asphalt. Furthermore, hemust pay $6.00 per ton freight, 95 and since 50% of this is paid for water, it will be observed that a municipality located some distance from the central refinery is virtually paying $36.00 per ton for the asphalt used in the construction of its roads. Obviously, a great saving could be effected if an asphalt could be treated at the refinery by adding reagents which would add only a negligible trifle to its weight, shipped in that condition to the distant point where it is to be applied to the road, and there emulsified. I have devised such a method.

The method by which the asphalt is treated at the refinery is illustrated by the following specific examples, but it is to be distinctly understood that the specific details given therein are not to be construed as placing any limitation on the scope of my invention.

Example I In emulsifying B grade asphalt I heat the same to 325 F. until it is thinly liquid, this operation being performed at the refinery. Into 1 ton of this molten asphalt I introduce 10 pounds of oleic acid; the mixture is thoroughly stirred and placed in tank cars for shipment. It will be noted that only A; of 1% of oleic acid is added to the asphalt, the reason being that quantities of oleic acid orv any other fatty acid which exceed 1% have, a deleterious effect on the asphalt, since they tend to increase its shortness. The as- .phalt arriving at the point where it is to be applied to the crushed rock in the construction of the road is heated to 212 F., simultaneously, in another container 5 pounds of caustic soda are dissolved in 1 ton of water and the solution heated to 212 F. The slowly flowing asphalt containing the oleic acid is poured into the hot caustic solution and the mixture thoroughly stirred. The emulsion hereby obtained is stable against dilution. An asphalt emulsion having any desired asphaltcontent may be prepared by altering the above proportions to give the desired concentration.

In order to more completely identify the asphalt which has been emulsified as above, the following physical and chemical characteristics are given:

(l) Specific gravity at 77 F.=1.05.

(2) Ductility over 100 centimeters per minute at 77 F. D C Standard Test).

(3) SolubilityCSg and CCL4 over 99.7.

(4) Loss in waterby heating at 325 F. for 5 hours one-half of one percent.

(5) Penetration, 50.

D grade asphalt is obtained in a thin liquid only by heating to 325 F. At 212 F. it is thick and viscous, having the consistency of 40 B., commercial sodium silicate. At F., "D grade asphalt is so rigidly solid that when struck a blow sembling the fracture of anthracite coal.

with a hammer, it is fractured in a manner re- The emulsion prepared according to this example contains 50% by weight of dispersed asphalt.

The D grade asphalts vary in penetration from 40 to 90. Therefore, a softening point by ball and ring method is from 110 to 130 F., and a point of thin liquefaction is from 300.to 325 F. where its specific gravity is approximately 1.0. In other words, "D grade asphalt which has a specific gravity greater than 1.0 at normal atmospheric tem erature, attains a specific gravity of 1.0 iat 300 to 325 F.', in which temperature range it is thinly liquid.

The emulsification of asphalts of the D grade type has been described in detail in this application because I believe that my method is novel, and it is to become the subject of a separate application. The .emulsification of asphalts having a liquefaction point above 212 F. has not, insofar as I am aware, been achieved without resorting to solvents such as kerosene, gasoline and the like, and wherein solvents have been used, they have never been wholly recoverable or do they ever wholly evaporate from the asphalt, thus they change the characteristics of the asphalt in which they are used. By the above method such asphalts may be emulsified without resorting to the use of solvents and with no change in the character of the asphalt. However, the emulsification of the low melting point asphalts has been worked out previously in connection with soaps and clays, and I believe it is necessary only to state that I modify prior practice to the extent of incorporating a fatty acid in the high melting point asphalts at the refinery and then ship them to the point where they are to be applied to the road. It is believed therefore from the complete description given in connection with the D grade asphalt, that an experienced operator will have no difficulty in applying my method to a low melting point asphalt which emulsifies much more readily than the high melting point. D grade asphalt.

In either case, I add not more than of 1% of a fatty acid to the asphalt at the lowest temperature at which it is thinly liquid and the quantity so used is insufficient to alter the charrefined, its specific gravity increases at atmospheric temperature to more than 1. Such a refined asphalt having a temperature of thin liquefaction above the boiling point of H20 may be emulsified by my process.

Prior to the application of the asphalt emulsion to the road undergoing construction, crushed rock of various sizes is of course first applied to the sub-grade in the usual: manner. Several courses of stone may be applied to the sub-grade and the surface layer leveled in the usual manner.

I may scatter over the surface of the crushed rock shredded redwood bark fibres having an average fibre length of about 3 inches. As an alternative method, I- may mix the bark fibres throughout the mass of the rock at any convenient point, either as it is spread over the subgrade or prior thereto. The amount of this fibre which I prefer to use is approximately 3 cubic feet, weighing a total of 27 pounds to 1 cubic yard of rock finally compacted. I next spray on to the combined aggregate an alum solution containing 20 pounds of aluminum sulphate per ton of solution. This is sufiicient for 10'tons of emulsion. The apshalt emulsion prepared as outlined above is immediately spread over the surface, and when it contacts with the alum sprayed fibre rock mixture a progressive de-emulsification ensues, the asphalt adhering to the aggregate surface while the water filters through or evaporates ofi'.

By progressively de-emulsification, I mean to imply that as the emulsion encounters the aggregate during its penetration into the mass thereof, it contacts the alum solution previously applied thereto and a separation of the dispersed asphalt from the water ensues with a deposition of the asphalt at the point of separation. Thus, the initial portion of emulsion is de-emulsified at the uppermost surface of the mineral aggregate and the asphalt deposited thereon, but the next succeeding portion of emulsion passes below this upper surface to the uppermost level exposing the alum solution coated surfaces, where the latter portion of emulsion is decomposed and the asphalt deposited. Thus all surfaces of the aggregate are coated with asphalt. A power roller'ls next passed over the asphalt coated aggregate of the pavement until a smooth, thoroughly compact, water resistant, resilient pavement is obtained.

The asphalt from the emulsion prepared according to my invention thoroughly coats the aggregates of the mass, firmly adhering to the surfaces thereof and effecting a wear-resisting, tenacious and resilient bond between the individual fragments thereof. I have found aluminum sulphate solution brings about an instantaneous de-emulsification of the asphalt emulsion. I have also found that the emulsion prepared according to my process is of the irreversible type and hence after the originally dispersed water of emulsion has evaporated or filtered through'into the interior of the earth, that the asphalt does not re-emulsify when in contact with water. asphalt emulsion will be obvious when one considers that in various parts of the country climatic conditions are such that frequently road pave- ;ments are subjected to extended periods of rainy weather, which would have the effect of reemulsifying a reversible type of emulsion, such for example as those emulsions prepared in conjunction with a dispersing agent such as soap or clay. In periods of continual rains, the asphalt which originated in a soap or clay emulsion is washed from the surface of the road and hence pavements constructed from this type of asphalt emulsion must be continuously repaired. On the other hand, my pavement is distinguished by its permanent character and its inertness to climatic variations.

As regards the amount of redwood bark fibre specified above, I wish to state that this may vary within wide limits both as regards the amount used and length of fibre. Thus I may use from 10 to 50 pounds of fibre of redwood bark per cubic yard of rock as finally compacted, and I may use fibres in length varying from an impalpable powder to those 3 inches long. While I prefer to use a 1% solution of alum, I may also use various other concentrations varying from 1 to 5%. I may use any soluble salt of a high metal in place of the alum solution.

In preparing the asphalt commercially and in quantity, the mechanical steps are invariably performed by laborers who have no conception of the scientific principles involved, and moreover are often so ignorant that they are incapable of adding the various ingredients in the proper amounts unless some scheme is provided by means of which the amount necessary to be added is indicated in the most elementary manner. If one were to direct a laborer of this type to add 0.7 of a pound of caustic soda to a ton of water, he would probably have no conception of what was meant by 0.7 of a pound. On the other hand, if the volume is increased to a size where it is substantial, he might possess sufiicient intelligence to enable him to divide the volume into 4ths and 5ths, at least approximately and satisfactorily for the purpose intended. In any event, by increasing the volume of a given mass greatly, his errors in manipulation are correspondingly diminished. I have devised a method whereby the caustic soda which is added in small amount may be procured in a form in which the laborer will be enabled to divide the same, without constant supervision, into the quantities which should be incorporated into the water. The method will be clear from the following explanation.

The advantages of my irreversible I prepare a block of caustic soda by dissolving 1135 grams of caustic soda in 113500. of colored water, hereinafter more fully described. I make a paste of 327 grams of cornstarch with 1262 cc. of water. I heat the starch solutionuntil the starch is obtained in colloidal solution and pour it into the caustic soda solution prepared as above, while constantly stirring the mixture. The temperature of the mixture is about 200 F. when the last portion of the starch solution is introduced. 0n cooling this mixture the mass solidifies without loss of volume and a block is obtained which contains sufficient caustic soda to emulsify 1,000 pounds of asphalt in 1,000 pounds of water.

The solid starch caustic soda cake has a combined weight of 6 pounds and it may be readily cut, and the most ignorant laborer should not have any difficulty in following instructions to the eifect that he should add A or or any other low denominator fraction, depending on the amount or quality of emulsion which is to be prepared.

In order to facilitate the optical examination of the dissolving of the above starch caustic soda, in water, I provide means whereby said dissolution may be continuously observed by introducing into the starch caustic soda cake mixture a coloring substance. I prepare this coloring substance by treating redwood bark with caustic soda in water. This material so produced is a water soluble modified xanthate. The caustic soda has the effect of withdrawing the coloring matter from the redwood bark when both are in aqueous solution, and imparting to the solution a deep red color. In preparing my coloring solution, I add that redwood bark dust which passes through 30 mesh screen to a 20% caustic soda solution in the proportions of 1 pound of bark dust to 9 pounds of caustic soda solution. The mixture is allowed to stand for several hours, all solid portions becoming soluble. This colored solution with about 30% additional caustic soda is used to dissolve in the preparation of the cake described above.

The laborer can determine complete dissolution in water of the starch caustic soda cake described above by noting the uniformity of color or lack of it, in the water solution of the said cake. In other words, the laborer adds the proper amount of cake to the water and agitates the solution until it is uniformly red in color, thus assuring in this critical step a sure method of gauging by sight the complete dissolving of the cake.

I claim:

1. A method of constructing asphaltic pavements which comprises applying crushed rock and redwood bark fibres to the subgrade, spraying the rock-fibre aggregate with an alum solution and then applying an irreversible asphaltic emulsion having a high melting point asphalt dispersed therein.

,2. The method of constructing asphaltic pavements which comprises applying crushed rock containing redwood bark fibres distributed throughout its mass to the subgrade, spraying the rock-fibre aggregate with an alum solution and then applying. an irreversible asphaltic emulsion having an asphalt dispersed therein which is thinly liquid only above 212 F.

3. The method of constructing asphaltic pavements which comprises applying crushed rock containing redwood bark fibres "distributed throughout its mass, spraying the rock-fibre aggregate with an alum solution and then applying an asphaltic emulsion having an asphalt dispersed therein, which has a point of thin liquefaction above 300 F. and which is emulsifiable at 212 F. without the use of asphalt solvents.

4. The method of preparing an asphaltic pavement which comprises applying crushed rock to s the sub-grade, spreading redwood bark fibres upon the said crushed rock, spraying the rockfibre aggregate with an alum solution and then applying an irreversible emulsion containing an asphalt having a high melting point dispersed therein.

5. The method of preparing anasphaltic pavement which comprises applying crushed rock to the sub-grade, spreading redwood bark fibres upon the said crushed rock, spraying the rock fibre aggregate with an alum solution and then applying an irreversible asphaltic emulsion having an asphalt dispersed therein which is thinly liquid only above 212 F.

6. The method of constructing asphaltic pave= ments which comprises applying crushed rock to the sub-grade, spreading redwood bark fibres upon the said crushed rock, spraying the rockcontaining shredded redwood bark distributed throughout its entire mass to the sub-grade, spraying the rock-fibre aggregate with an alum solution and then applying an asphaltic emul- 'sion, the asphalt of which has been previously processed -by heating an asphalt of the B grade type to above 300 F., and adding a small amount of a fatty acid whereby the said D grade type is rendered emulsifiable in water at 212 F.

8. A method of making pavements and the like consisting of spreading a layer of mineral aggregate, spraying the same with an alum solution and thereafter spraying the layer with an irreversible asphaltic emulsion which will break upon contact with the alum.

FRANCIS L. CARSON. 

